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From: Tejun Heo <tj@kernel.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Michal Koutný" <mkoutny@suse.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Hillf Danton" <hdanton@sina.com>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Marco Elver" <elver@google.com>,
	"Zefan Li" <lizefan.x@bytedance.com>,
	tglx@linutronix.de
Subject: Re: [PATCH v4 4/6] kernfs: Don't re-lock kernfs_root::kernfs_rwsem in kernfs_fop_readdir().
Date: Mon, 27 Jan 2025 08:01:51 -1000	[thread overview]
Message-ID: <Z5fKD1AsqkgDLjox@slm.duckdns.org> (raw)
In-Reply-To: <20250127090200.lEQ2Igag@linutronix.de>

On Mon, Jan 27, 2025 at 10:02:00AM +0100, Sebastian Andrzej Siewior wrote:
> On 2025-01-24 13:15:32 [-1000], Tejun Heo wrote:
> > Hello,
> > 
> > On Fri, Jan 24, 2025 at 06:46:12PM +0100, Sebastian Andrzej Siewior wrote:
> > ...
> > > to avoid holding a global lock during a page fault. The lock drop is
> > > wrong since the support of renames and not a big burden since the lock
> > > is no longer global.
> > 
> > It's still a pretty big lock. Hopefully, at least name accesses can be
> > converted to rcu protected ones later?
> 
> Not sure what you mean by "rcu protected ones". The name is already RCU
> protected which is part of the problem :P
> Assuming an upper length of name to be around 255 and
> kernfs_fop_readdir() to be very early on the chain then we could copy
> the name on stack within the RCU section and do this without
> ::kernfs_rwsem.

Please ignore me on this one. I'll take a better look next round.

Thanks.

-- 
tejun

  reply	other threads:[~2025-01-27 18:01 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-01-24 17:46 [PATCH v4 0/6] kernfs: Use RCU to access kernfs_node::{parent|name} Sebastian Andrzej Siewior
2025-01-24 17:46 ` [PATCH v4 1/6] kernfs: Acquire kernfs_rwsem in kernfs_notify_workfn() Sebastian Andrzej Siewior
2025-01-24 23:09   ` Tejun Heo
2025-01-24 17:46 ` [PATCH v4 2/6] kernfs: Acquire kernfs_rwsem in kernfs_get_parent_dentry() Sebastian Andrzej Siewior
2025-01-24 23:11   ` Tejun Heo
2025-01-27  8:42     ` Sebastian Andrzej Siewior
2025-01-24 17:46 ` [PATCH v4 3/6] kernfs: Acquire kernfs_rwsem in kernfs_node_dentry() Sebastian Andrzej Siewior
2025-01-24 23:12   ` Tejun Heo
2025-01-24 17:46 ` [PATCH v4 4/6] kernfs: Don't re-lock kernfs_root::kernfs_rwsem in kernfs_fop_readdir() Sebastian Andrzej Siewior
2025-01-24 23:15   ` Tejun Heo
2025-01-27  9:02     ` Sebastian Andrzej Siewior
2025-01-27 18:01       ` Tejun Heo [this message]
2025-01-24 17:46 ` [PATCH v4 5/6] kernfs: Use RCU to access kernfs_node::parent Sebastian Andrzej Siewior
2025-01-24 23:35   ` Tejun Heo
2025-01-27 16:25     ` Sebastian Andrzej Siewior
2025-01-27 18:00       ` Tejun Heo
2025-01-24 17:46 ` [PATCH v4 6/6] kernfs: Use RCU to access kernfs_node::name Sebastian Andrzej Siewior
2025-01-24 23:41   ` Tejun Heo
2025-01-27 16:17     ` Sebastian Andrzej Siewior

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